『Abstract
　Two-year (June 2003-May 2005) precipitation samples were collected from three monitoring sites with similar economy development level in the Yangtze River Delta Region of China to investigate the spatial-temporal variation of inorganic N wet deposition. The results showed that the Yangtze River Delta Region had higher inorganic N wet deposition than the northwestern, northern, or southern China. There was spatial variation of inorganic N wet deposition. The positive relationship between inorganic N deposition and precipitation suggested that rainfall amount might be an important factor influencing the wet deposition of inorganic N. Deposition of inorganic N occurred mainly in the spring and summer season (March-August; 70％ of the annual total), which was in accord with seasonal distribution of precipitation. However, a negative logarithmic relation between rainfall and inorganic N concentration in rainwater indicated the dilution effect of rainwater on inorganic N concentration. Distinguished variation of NH4⁺/NO3^- ratio in wet deposition existed in the different time scale. NH4⁺/NO3^- ratio evidently decreased from 6 in 1980s to 1.2 in 2003/2005 and greatly varied between 0.3 and 9.9 within a year. NH4⁺/NO3^- ratio peaked in accordance with nitrogen-fertilizing time during crop growing season. Annual alternate appearance of the ¹⁵N-enriched and ¹⁵N-depleted periods coincided with the temporal variation of NH4⁺/NO3^- ratio, which was closely related to the timing of fertilization and seasonal climate changes, suggesting the effect of NH4⁺ sources in the wet deposition.

Keywords: NH4⁺/NO3^- ratio; Nitrogen isotope; Source of NH4⁺; Variation; Wet deposition』

1. Introduction
2. Materials and methods
　2.1. Study sites
　2.2. Sampling and analysis
3. Results and discussion
　3.1. Spatial variation of inorganic nitrogen in wet deposition
　3.2. Temporal variation of inorganic nitrogen wet deposition
　　3.2.1. Comparison of inorganic nitrogen wet deposition in the early 1980s with that between 2003 and 2005
　　3.2.2. Seasonal patterns of inorganic nitrogen wet deposition
　　3.2.3. Effect of nitrogen fertilization during crop growing season on temporal variation of NH4⁺/NO3^- ratio in precipitation
　3.3. Effect of nitrogen fertilization during crop growing season on temporal variation of δ¹⁵NH4⁺ value in precipitation
4. Conclusion
Acknowledgments
References